ASTM_D_1872_-_82_scan.pdf

Designation:D 1872-82 Nti AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race St.,Philadelphia,Pa.19103 Reprinted from the Annual Book of ASTM Standards,Copyright ASTM If not listed in the current combined index,will appear in the next edition.Standard Method o f Testing MERCAPTOBENZOTHIAZOLE IN BENZOTHIAZYL RUBBER CHEMICAL-FREE 2-DISULFIDE This standard is issued under the fixed designation D 1872;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(E)indicates an editorial change since the last revision or reapproval.1.Scope 1.1 This method covers a procedure for the measurement of the toluene-soluble acidic im-purities in benzothiazyl disulfide(MBTS).2.Applicable Document 2.1 ASTM Standard:D 3040 Practice for Preparing Precision Statements for Standards Related to Rub-ber and Rubber Testing2 NOTE 1-The specific dated edition of Practice D 3040 that prevails in this document is referenced in the Precision section.3.Summary of Method 3.1 The MBTS is dissolved in hot toluene and crystallized out by chilli g.The filtered extract is titrated in a noneCdcous medium,using sodium methoxide as the titrant and thymol blue as the indicator.4.Significance and Use 4.1 2-Mercaptobenzothiazole(MBT)is usu-ally the major impurity in MBTS.Free MBT in MBTS may be determined by this method.4.2 MBT and MBTS are used for rubber and latex vulcanization acceleration.The amount of MBT in MBTS may be of impor-tance in predicting performance in rubber com-pounds and for raw material purchase and control.4.3 This method may be used as a quality-control tool and for research and development work.5.Apparatus 5.1 Iodine or Erlenmeyer Flasks,250-cm3.5.2 Filter Funnels,sintered glass,medium 5.3 Magnetic Stirring Apparatus.5.4 Buret,semimicro,10-cm3.porosity,76-mm(3-in.).6.Reagents 6.I Purity o f Reagents-Reagent grade chemicals shall be used in all tests.Unless otherwise indicated,it is intended that all re-agents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society,where such spec-ifications are aailable.Other grades may be used,provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.6.2 Sodium Methoxide,Standard Solution(O.I N)-Wash approximately 5 g of freshly cut sodium metal with methanol and dissolve in 100 cm3 of absolute methanol in a hood,away from flames.The reaction can be controlled by occasionally cooling the reaction vessel in ice water.When the reaction is com,plete,add 150 cm3 of methanol and 1500 cm3 of toluene.Store the reagent in a borosilicate glass container This method is under the jurisdiction of ASTM Com-mittee D-1 1 on Rubber and is the direct responsibility of Subcommittee D 11.1 1 on Chemical Analysis.Current edition approved Oct.29,1982.Published Janu-ary 1983.Originally published as D 1872-61 T.Last pre-vious edition D 1872-79.1983 Annual Book of ASTM Standards,Vols 09.01 and 09.02.“Reagent Chemicals,American Chemical Society Spec-ifications,”Am.Chemical Soc.,Washington,D.C.For sug-gestions on the testing of reagents not listed by the American Chemical Society,see“Reagent Chemicals and Standards,”by Joseph Rosin,D.Van Nostrand Co.,Inc.,New York,N.Y.,and the“United States Pharmacopeia.”1 NOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.protected from carbon dioxide and water.Standardize the solution as follows:6.2.I Weigh accurately O.1 g of benzoic acid(National Bureau of Standards)into a 250-cm3 iodine flask and dissolve in 100 to 150 cm3 of toluene.Titrate with the sodium methoxide solution,using a magnetic stirrer,to a thymol blue end point.Use a IO-cm semimicro buret for the titration and allow the buret to drain very slowly to reduce drainage error.Titrate in a like manner the volume of solvent used to determine the blank titration.Calculate the molarity as follows:M=A/I(B-C)X 0.122121(1)where:A B-C 0.12212=grams of benzoic acid used,cubic centimetres of sodium meth-oxide solution required for titration of the benzoic acid solution,cubic centimetres of sodium meth-oxide solution required for titration of the blank,and milliequivalent millimole mass of benzoic acid.6.3.Toluene.D 1872 8.2 Transfer the flask to an ice bath.Chill the flask and its contents to O to 5C with occasional swirling.8.3 While cold,filter through a 76-mm(3-in.),medium-porosity filter funnel,using vac-uum,catching the filtrate in a 250-cm3 vac-uum flask.Wash the iodine flask once with 10 cm3 of toluene,and add the flask washings to the MBTS on the filter.8.4 Add 5 drops of thymol blue indicator solution to the filtrate in the filter flask and titrate with the 0.1 M sodium methoxide so-lution,using a magne